Armour, either in the form of plates of metal or chain mail with its many interlocked rings, is the primary attribute and symbol of the warrior. As such, several of the classical deities are often depicted wearing armour.

Peter Paul Rubens painted The Triumph of Victory in about 1614 for the Antwerp Guild of St George, its organisation of archers. Mars in his short suit of black armour dominates, his bloody sword resting on the thigh of Victoria, the personification of victory. She reaches over to place a wreath of oak or laurel on Mars, and holds a staff in her left hand. At the right, Mars is being passed the bundle of crossbow bolts that make up the attribute of Concord. Under the feet of Mars are the bodies of Rebellion, in the foreground, who still holds his torch, and Discord, on whose cheek a snake is crawling. The bound figure resting against the left knee of Mars is Barbarism.

Jacob Jordaens’ finished version of an original sketch by Rubens now known as The Golden Apple of Discord (1633) shows the wedding feast of the deities where Eris (Discord) makes her gift of the golden apple to set up the Judgement of Paris, leading to the Trojan War. At the left, Athena/Minerva, wearing her plumed helmet and a suit of ornate plate armour, reaches forward for that apple.

Just to confuse, the Roman goddess of war, Bellona (Greek Enyo), is also shown in or with armour by convention.

Peter Paul Rubens’ undated Portrait of Marie de’ Medici as Bellona shows her in the midst of cannon, arms and armour, with an exuberantly decorated helmet, a sceptre and a statue of a winged woman.

Armour inevitably plays a role in some of the events reported during the war against Troy. After his close friend Patroclus had been killed while wearing the armour of Achilles, he demanded a fresh suit made by Vulcan/Hephaestus before he would return to engage in battle.

Anthony van Dyck’s Thetis Receiving the Weapons of Achilles from Hephaestus from about 1630-32 shows the scene when Thetis is collecting her son’s new armour from Hephaestus, at the left.

Benjamin West’s Thetis Bringing the Armour to Achilles from 1804 shows the Greek warrior being presented with the armour and helmet by his mother Thetis.

When Achilles is killed in battle, in accordance with warrior tradition, his armour was handed on to the next in line, who could have been either Ajax or Odysseus.

Leonaert Bramer’s small painting on copper of The Quarrel between Ajax and Odysseus was made between about 1625-30. The pair stand in their armour, next to tents pitched at the foot of Troy’s mighty walls. At their feet is the armour of Achilles, and all around them are Greek warriors, some in exotic dress to suggest more distant origins.

Armour also leaked through into Christian religious paintings.

Lucas Cranach the Younger sets The Conversion of Saul (1549) in mediaeval northern Europe, with Paul and his party riding knightly chargers in their armour. Paul’s horse has fallen to the ground, with Paul still in the saddle rather than prostrate on the ground. Paul holds his hands up and looks to the heavens, where the figure of Christ is seen in a break in the clouds at the top left corner.

It was the young French martyr Joan of Arc, though, who is most often depicted wearing armour.

JAD Ingres painted Joan of Arc at the Coronation of Charles VII, in Reims Cathedral (1854). She stands close to the crown, resplendent in full armour and holding a standard, the two-pointed oriflamme embroidered for her by the women of Orléans, in her right hand.

The second scene in Jules Eugène Lenepveu’s Joan of Arc Murals (1886-90) shows Joan leading the French forces against the English, who were laying siege to the French city of Orléans. There had been controversy in Joan’s trial as to whether she had used weapons against the English; Lenepveu hedges here, showing her holding a sword in her right hand, but brandishing the Dauphin’s standard to rally the French, in the role that she described of herself. She’s wearing a suit of plate armour, which she was provided with in preparation for this operation. As this would have been designed to fit a man, this was part of the case against her for ‘cross-dressing’ in men’s clothes.

Lovis Corinth is one of several major painters who acquired themselves a suit of armour. This featured in two symbolic paintings made before and after the First World War.

When war broke out on 28 July 1914, Lovis Corinth and most of the other artists in Berlin shared an enthusiastic patriotism that initially gave them a buoyant optimism. He expressed this openly in his In Defence of Weapons from 1915.

Armour Parts in the Studio is Corinth’s summary of Germany’s defeat in 1918. The suit of armour is now empty, broken apart, and cast on the floor of his studio.

Unlike watercolour, oil paint ‘dries’ by an irreversible process of chemical polymerisation. Once ‘dried’ it resists solvents and can be painted over without any risk of its pigments mixing between layers. Unlike modern acrylic paints, oil paint usually takes at least a week or two before its surface is dry, so allows the painter to control mixing of an existing layer with fresh paint. Skilful control of paint viscosity and drying rate thus gives fine control over the softness of edges and their blurring or sharpness.

This is illustrated well in Lucas Cranach the Elder’s portrait of Salome with the Head of Saint John the Baptist from about 1530. Crisp edges appear where you expect, for example between skin and clothing. In some places, he also outlined edges with thin lines of dark shadow for emphasis. Where skin tone changes more subtly, and in Salome’s eyebrows, there are soft transitions achieved by painting wet on wet and blurring the edge, a technique often known as sfumato, as seen in the detail below.

Cranach and the staff of his workshop would have worked on that painting over a period of many weeks to achieve those effects. In contrast, sketching with oil paints in front of the motif is far simpler, and on a more modest scale. Because of constantly changing light and shadow, most proficient landscape artists aim to complete their oil sketches in under two hours, and an hour is ideal.

Robert Henri’s Landscape Sketch at Escorial (1906) was painted on a wooden pochade panel, almost certainly in a single short session outside the city of Madrid, in the hills near the Escorial. Although he used the viscosity of different paints to make its skyline sharp, you can see where his coarse brushstrokes have been applied and colours mixed and laid in streaks.

The young Canadian artist Tom Thomson excelled in rapid sketching in oils, with several witnessed accounts of him dashing off a painting in little more than fifteen minutes. As a result he was able to capture many transient effects, such as the passing thunderstorm in Thunderhead from 1912-13. He has found it harder to keep a crisp skyline, and clearest separation of paint is in the white masts of the boats at the edge of the water. Those were painted last, in single strokes with as little diluent as possible.

Before the nineteenth century, quick oil sketches were almost never shown to the public, but used by masters including Valenciennes and Constable purely as preparative studies. When fashions changed, it became acceptable if not desirable for paintings to look sketchy and rushed, although appearances can sometimes be deceptive.

Some masters of fast painting used these skills in multiple sessions, to increase the amount of detail they could incorporate into a landscape. When Pissarro suffered from eye problems late in his career, he painted from rooms with views over the streets of Paris, and produced some of his finest cityscapes.

Boulevard Montmartre, Spring Morning (1897) is composed primarily of buildings and streets, a plethora of figures, and countless carriages to move those people around, the ingredients for so many of his late paintings.

In the foreground, Pissarro may have formed each quite roughly, but he has painted in sufficient detail. Three white horses range in tone and colour, with highlights on the front of each head. You can see which people are wearing hats, and spot ladies in their fashionable clothing.

Deeper into the distance, detail is lost, and the carriages and crowds merge into one another. Still they have a rhythm, highlights and shadows, and form. He must have spent day after day at his hotel window populating these busy streets.

Other Impressionist paintings appear at first sight to have been painted quickly in front of the motif, but were more likely worked on over a period of months in the studio. Once the public had come to expect an Impressionist painting to look as if it had been painted quickly, they expected the same look even though some paintings may have required several months painting.

Monet’s Flowering Plum Trees (1879), for example, has a complex structure in its paint layer, as seen from the surface in the detail below. Some marks have been added wet-in-wet, but many wet-on-dry, demonstrating it must have been worked on over a period of weeks or months.

The myth about Monet’s Grainstacks series is that they depict transient effects of season, weather, and light, as they were painted en plein air over the course of the winter. Looking at all twenty-five, I have long had my doubts, and suspect that Monet spent a lot of the time prior to their exhibition making further changes to them. This in no way lessens Monet’s sublime achievement, nor their art in any way. It’s just that they aren’t quite the paintings described by the myth that has grown around them.

Looking at Grainstacks, End of Summer, considered to be one of the earliest in the series and numbered 1266, the trees behind the two grainstacks are still in full summer leaf, with no indication of the advent of autumn. Yet Monet’s signature gives the year as 1891. Looking at its paint surface in detail (below), some has been applied wet-in-wet and blended with underlying and adjacent paint, but many other brushstrokes have clearly been applied over dry underlayers.

The blue-grey shadow of this grainstack was applied with relatively dilute paint wet-on-dry over thicker off-white paint with marked surface texture. However, that off-white paint has itself been applied wet-on-dry over a pale green layer. This couldn’t have been achieved in the same day, even when the ambient temperatures were warmer during the early autumn, but probably reflects at least three sessions with drying time in between them.

Grainstack, Sun in the Mist, numbered 1286, is thought to be one of the later paintings in the series, apparently showing the sole remaining grainstack in the Spring of 1891. It too has multiple layers applied wet-on-dry, with many hatched brushstrokes in shades of orange and pink apparently applied over a well-dried surface. These are again shown well in the detail (below) of the grainstack itself.

At the right side of the foot of the grainstack, the lowest layer of paint consists of dull blue and green that appear to have been applied at about the same time and have blended in places. When that layer had dried, infrequent and relatively thick streaks of white were added wet-on-dry. When that had dried, brown-orange was applied to form the uppermost layer. That uppermost layer has also been used to remodel the form of the grainstack using thickly-applied flesh, pale yellow and orange paint.

The evidence points to Monet starting each of this series with a sketch using more dilute paint in front of the motif in the circumstances described in the title. He then brought each canvas into his studio, where he continued to work on it, making further adjustments, adding partial layers of paint, and tweaking each work in comparison to the others in the series. This would have taken place over a period of several weeks: in the case of the canvases that he had started at the end of the summer of 1890, such as W1266 above, that period could have amounted to six months.

That may well have been longer than the time taken by Cranach to paint Salome.